1. Field of the Invention
The present invention relates to methods for making wear resistant polymeric materials. Methods of making medical implants containing antioxidant-containing wear resistant polymers and materials used therewith also are provided. Wear resistant polymeric materials and medical implants containing such materials are also provided.
2. Description of the Related Art
It is advantageous to have tough and ductile polymeric materials, for example, ultrahigh molecular weight polyethylene (UHMWPE), for total joint implants without sacrificing oxidative stability and wear resistance. Wear resistance can be improved by cross-linking. However, crosslinking reduces the toughness and ductility of the material. Therefore, it is desirable to have a method to increase toughness and ductility of wear and oxidation resistant polymeric material.
Antioxidant stabilization of various cross-linked polyethylenes has been described. Schaffner (U.S. Pat. No. 6,277,390) described a disperse formulation of UHMWPE blended with vitamin E as an antioxidant and sterilized by ionizing irradiation, but he did not disclose any information neither on a UHMWPE formulation protected against oxidation in the long term nor one that has a limited crosslinking on the surface. McKellop (U.S. Pat. No. 6,494,917) described methods of low energy irradiation to limit cross-linking on the surface but he did not disclose neither methods of making highly oxidation resistant polymeric material by antioxidants nor methods of making antioxidant-stabilized materials. Lindgren (U.S. Pat. No. 6,448,315) described methods of blending UHMWPE with antioxidant and further gamma irradiation but did not disclose methods of low energy irradiation nor other methods of antioxidant incorporation after irradiation. Muratoglu (U.S. Pat. No. 7,431,874) disclosed methods of making antioxidant-stabilized materials by doping polymeric material with antioxidants after radiation crosslinking but taught against the inclusion of the antioxidant before cross-linking.